It is known to employ a pressure-sensitive interrupter device as a cover on a capacitor. Such a device then serves to break electrical connection should the interior of a can housing the capacitor be subjected to excessive pressure. UK patent specification No. 1592706 describes a known form of such a device. UK patent specification No. 1441507 also describes a capacitor in which a cut-out device responds to deformation of the capacitor element itself in the event of a rise in internal pressure.